McIntosh MC-75 in unknown condition, what do I do?

Oops! The first sentence of the last paragraph of my preceding post should have read:

Apply the polish with cloths or cotton swabs, being very careful NOT to get any of it on the lettering, and being careful not to get it into crevices from which you may not be able to wipe off the residue

-- Al

That is a valuable and highly prized collectable that you rescued!

The value is highly sensitive to cosmetic condition, however. A stereo pair of these amps with near-mint cosmetics and excellent chrome would easily command several thousand dollars, and possibly much more. However, poor chrome reduces the value drastically. And one amp is worth considerably less than one-half the value of a pair, for obvious reasons which you alluded to.

Obviously finding another one, especially at a reasonable price, will be difficult and require patience. All I can suggest is watching the offerings here, at eBay, etc.

You are correct to be cautious about powering it up. Vintage equipment, especially equipment which might not have been previously powered up in a long time, should have its ac power brought up slowly, over a period of several hours or more, by means of a variac or other variable ac power supply. That will allow the electrolytic capacitors to "reform," and will allow overheating or other problems to be detected before more serious secondary damage occurs.

Here is a little bit of info on it. A little Googling will turn up much more.

http://www.roger-russell.com/amplif1.htm#mc75

Best of luck with the great find!

-- Al

Also, I'd suggest not operating it without a speaker load. That might result in higher than normal internal operating voltages, which could overstress capacitors or other internal components. I use a $10 or so Radio Shack speaker driver when I do initial test and troubleshooting of older amplifiers.

Regards,
-- Al

Outstanding!

It's a bit like being given a Ferrari with a bad transmission.

In the meantime, remember, there's someone out there in exactly the same situation as you -- just waiting for YOU to give up first !!

Very well put, in both cases! :)

-- Al

It would obviously be desirable to run the tubes across a tube tester, but if you don't have access to one I think it should be safe to try the amp without first testing the tubes, PROVIDED that you use a variac or equivalent to bring up the voltage very slowly, as I described. While you do that, look for any reddening of the plates in the tubes, as well as excessive warming of the transformers, and of any electrolytic capacitors which may be on top of the chassis. Obviously, don't go underneath the chassis unless you know exactly what you are doing, or there is an electrocution risk, even for some time after power is removed.

To help the chrome on similar vintage components, I've simply used commonly available metal polishes which list chrome as one of the metals they are suitable for. Such as Noxon, which you can find at supermarkets and hardware stores. There are also chrome-specific polishes, used for automotive and motorcycle purposes, but I'm not particularly familiar with them.

Apply the polish with cloths or cotton swabs, being very careful to get any of it on the lettering, and being careful not to get it into crevices from which you may not be able to wipe off the residue. Then wipe it off as directed.

Regards,
-- Al